1. Field of the Invention
The present invention relates to a battery voltage regulator for vehicles for controlling energization of a vehicle generator, and more particularly to a battery voltage regulator executing the above operation in response to a voltage which appears at a juncture between the collector of a lamp drive transistor and a charge lamp connected to a battery through a series-connected key switch.
2. Brief Description of Prior Art
To control the excitation of the field winding in response to an output of a voltage regulator, wherein a voltage regulating circuit of the voltage regulator for controlling battery voltage to a desired value is energized by a battery, the voltage regulator must have an external terminal through which a key switch is connected to the battery. The voltage regulator is disconnected from the vehicle battery by the key switch when the vehicle engine is not in operation in order to prevent discharge of the battery through the regulator circuit and various electrical loads. In addition, there must be provided another external terminal if a charge lamp is provided for warning when the generation of power is stopped for some reason.
On the other hand, regulator circuits have now been reduced in size by utilizing IC technology, however, this has caused a relative increase in the ratio of the area occupied by the external terminals, electrically connecting the regulator with the external circuits, to the size of the regulator casing. Therefore, it is an urgent need to provide a compact regulator which requires a minimum number of external terminals or conductors from the key switch. In order to meet such requirements, Japanese unexamined patent application No. 58-215,715 proposes a solution, which provides just one common external terminal to which the key switch and the change lamp are connected in series with the battery, thus reducing the external terminals in number.
The above mentioned regulator is composed of a combination of the key switch and the charge lamp in series, one end of which is connected to the positive terminal of the battery and the other end to the aforementioned common external terminal. The voltage regulating circuit is supplied power for the first time to maintain the battery terminal voltage at a desired set value when a terminal voltage detecting circuit detects the voltage value which appears at the common external terminal, which is higher than a predetermined value. The terminal voltage detecting circuit comprises a transistor connected to the common external terminal, so that if the key switch becomes leaky, this will prevent leakage current from flowing through the transistor and will prevent a relatively high voltage between the common external terminal and ground, which would cause the terminal voltage detecting circuit to erroneously operate the voltage regulating circuit in spite of the fact that the key switch is not actually activated yet.
Moreover, even during normal operation of the charging system, if eventual failure of the charge lamp or a break in the lamp conductor occurs, this may cause a problem in that the power supply to the voltage regulating circuit will be stopped with a sudden drop in voltage accross the common external terminal. This problem results in malfunction of the terminal voltage detecting circuit because of the low terminal voltage, almost zero at the common terminal, with no power generation from the generator.